Okay I said I'd update.
So as PeakT also said, probably a 10% or less difference in results from different labs, but for Total testosterone. Free Testosterone can not really be compared.
I was told "As long as the results are measured in the same units, reference ranges have no real effect on the relevance of the results. They're merely based on the fact that those two labs have different accumulated data from their patients, which average out differently. They build those reference ranges based on their customers averages, so it's very common for them to be different."
Got my results back from LabCorp:
Total = 473 ng/dL (264-916 ng/dL)
Free = 10.2 pg/mL (9.3 - 26.5 mg/dL)
Very slowly are my levels continuing to rise. Not a fast improvement, but still improvement. General well-being, energy, and everything else is continuing to get better. Only supplements I am taking are multi-vitamin, vitamin D, & fish oil along with strategic exercise & diet. Going to get a complete micronutrient test next and fix any deficiencies I may have, which I'm sure I do.
Will go back next month to Quest and probably continue to stay at Quest as it's faster than LabCorp.